1. Field of the Invention
The present invention relates to a hydrodynamic seal composed of a fluorine resin.
2. Description of the Prior Art
As the conventional seal composed of a fluorine resin, there is known a seal having a structure as shown in FIG. 7, which comprises a ring-shaped annular thin plate 20 composed of a fluorine resin, the outer peripheral portion 21 of said thin plate 20 being gripped and supported by an L-shaped outer ring 22 and an L-shaped inner ring 23 to bend the thin plate 20 substantially at the center thereof and a spring 27 being fitted in an annular recess 26 formed on the back face of a lip portion 25 formed on the inner peripheral portion 24 of said thin plate 20. In a conventional seal of this type, a good chemical resistance can be expected since the annular thin plate 20 per se is composed of a fluorine resin, but since the spring 27 is exposed to the outside, the spring 27 is promptly corroded and its function of imparting an elasticity to the lip portion is lost. In addition to this defect, this conventional seal involves a problem that processing for forming a screw groove on the lip portion is very difficult and the processing cost is increased.